Properties:

The style the button should handle. Allowed values are:Object as described by http://docs.ckeditor.com/#!/api/CKEDITOR.style.String pointing to an object inside the editor instance configuration. For example, style = 'coreStyles_bold' will try to
retrieve the style object from editor.config.coreStyles_bold. Nested properties such as style = 'myplugin.myConfig.myStyle'
are also supported and will try to retrieve the style object from the editor configuration as well.